In the past, the vacuum hoses used with high temperature ovens and autoclaves have not been entirely satisfactory. One common hose used in this environment is formed by a Teflon tube enclosed by a braided metal sheath. In addition to being expensive to manufacture, the frequent flexing and twisting of such hoses that occurs when they are being used causes the metal sheath to become frayed and the Teflon tube to break or collapse. The breaking and/or collapsing of the Teflon tube results in a loss of vacuum. Frayed metal sheathing makes such hoses difficult to handle because the frayed metal is prone to cut the handler. One approach to strengthening braided metal sheathed Teflon tube hoses has been to include a metal coil spring inside the hose. Attempts to prevent fraying of the braided metal sheath involved coating the sheath with materials such as neoprene and vinyl materials. These materials were found to be unacceptable because they crack when exposed to high temperatures, resulting in the exposure and fraying of the braided metal sheath. A follow-up approach has been to enclose the hose with an external metal coil spring. While these additions improve hose wear resistance, they have made the resultant hoses more expensive and heavier. Further, the addition of strengthening coils does not eliminate other disadvantages of braided metal sheathed Teflon tube hoses. Specifically, the braided metal sheath of such hoses requires that the hose be swagged to connectors. Swagging is an expensive, time-consuming procedure. In addition, because metal has low thermal capacity and high thermal conductivity braided metal sheaths and protective metal coils store large amounts of heat when placed in an oven or autoclave. Because the metal sheaths and outer metal protective coils store large amounts of heat, braided metal sheathed Teflon hoses are difficult to handle immediately after removal from an oven or autoclave. They cause burns and become broken when the amount of stored heat causes them to be dropped.
One attempt to solve the foregoing problems involved creating a hose by spirally wrapping a fabric reinforced uncured silicone elastomeric sheet around a mandrel to form a tube and, then, vulcanizing the elastomer. Such hoses were found to be unacceptable because the reinforcing fabric, which extended from the interior to the exterior of the hose, wicked and created a gas path via which vacuum is lost. In order to avoid this difficulty, the addition of a Teflon liner was proposed. While the Teflon liner avoided the vacuum loss problem, it created other problems. Specifically, flexing and twisting of the tube when in use resulted in the Teflon liner collapsing and breaking.
This invention is directed to providing fiber reinforced silicone elastomer hoses that avoid the foregoing disadvantages of prior hoses designed for use in ovens and autoclaves. While hoses formed in accordance with the invention were designed for use in ovens and autoclaves, it is to be understood that they can also be used in other environments.